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A general set of time-domain equations describing linear sound propagation in a rigid-frame, gas-saturated porous medium is derived. The equations, which are valid for all frequencies, are based on a relaxational model for the viscous and thermal diffusion processes occuring in the pores. The dissipative terms in the equations involve convolutions of the acoustic fields with the impulse response of the medium. It is shown that the equations reduce to previously known results in the limits of low and high frequencies. Alternative time-domain equations are also derived based on a Padé approximation.

The plot of the transmission coefficient moduli cannot be used to analyze all the resonances of layered structures because of the overlapping of the resonances. A method using the scattering matrix eigenvalues is presented. It allows, first, to annihilate the overlapping and to recover the resonance positions and half-widths and second, to divide in two independent sets most of the resonances involved in symmetric structures as well as in nonsymmetric ones. Comparisons between the results provided by the method and those coming from the poles of the transmission coefficient agree. In many cases, the transition terms constitute a generalization of the transmission coefficients.

Recent results have shown that auditory localization in the horizontal plane is dramatically worse for listeners wearing double hearing protection (earplugs and earmuffs) than it is for listeners wearing single hearing protection (earplugs or earmuffs alone). This suggests that double hearing protection might also impair the spatial unmasking that normally occurs when two simultaneous talkers are spatially separated in azimuth (the so-called “cocktail party” effect). In this experiment, normal hearing listeners wearing no hearing protection, single hearing protection (earmuffs), or double hearing protection were asked to perform a speech intelligibility task that required them to segregate two simultaneous talkers who were either presented from the same loudspeaker or spatially separated by 90° in azimuth. The listeners were also asked to determine the location of the target talker in each trial. The results show that the listeners were unable to reliably determine the location of the target talker when they wore double hearing protection, but that they were still able to benefit from the spatial separation of the competing talkers. This suggests that the use of double hearing protection causes spatially separated sound sources to be heard at locations that are inaccurate but still distinct enough to enhance the segregation of speech.

By using an experimental approach, the acoustic backscattering from air-filled cylindrical shells, immersed in water, is investigated. The targets considered in this work are ended either by hemispherical caps or by flat circular lids. Given the 1% shell thickness and the frequency window of this study, only echoes resulting from the propagation of and waves (respectively, quasi-compressional and quasi-shear waves of lowest order) are observable. On both types of objects, measurements are carried out at various aspect angles of incidence over the broadside of the target. The influence of the type of end-caps on the propagation of helical waves (i.e. waves initially generated on the cylindrical part of the objects) is studied using incidence-angle/time representations.

Vowel production in gay, lesbian, bisexual (GLB), and heterosexual speakers was examined. Differences in the acoustic characteristics of vowels were found as a function of sexual orientation. Lesbian and bisexual women produced less fronted /u/ and /ɑ/ than heterosexual women. Gay men produced a more expanded vowel space than heterosexual men. However, the vowels of GLB speakers were not generally shifted toward vowelpatterns typical of the opposite sex. These results are inconsistent with the conjecture that innate biological factors have a broadly feminizing influence on the speech of gay men and a broadly masculinizing influence on the speech of lesbian/bisexual women. They are consistent with the idea that innate biological factors influence GLB speechpatterns indirectly by causing selective adoption of certain speechpatternscharacteristic of the opposite sex.

Pods of the little known pygmy killer whale (Feresa attenuata) in the northern Indian Ocean were recorded with a vertical hydrophone array connected to a digital recorder sampling at 320 kHz. Recorded clicks were directional, short (25 μs) transients with estimated source levels between 197 and 223 dB 1 μPa (pp). Spectra of clicks recorded close to or on the acoustic axis were bimodal with peak frequencies between 45 and 117 kHz, and with centroid frequencies between 70 and 85 kHz. The clicks share characteristics of echolocation clicks from similar sized, whistling delphinids, and have properties suited for the detection and classification of prey targeted by this odontocete.

Reciprocity, energy conservation, and time-reversal invariance are three general properties of the wave fields that imply algebraic scattering matrix properties. In this paper, these scattering matrix properties are established for waveguides when evanescent modes are taken into account. The situations correspond to guided acoustic pressurewaves in fluids and Lamb waves in solids treated with the same formalism. The relations between the three properties verified by the scattering matrix are then discussed, and it is found that, as soon as two properties are verified, the third is also verified.

In the present paper we are concerned with sound propagation and attenuation in two- or three-dimensional lined bends. First it is shown that the effect of locally reacting absorbing materials at the walls of a waveguide can easily be taken into account in the multimodal formulation proposed in earlier papers by the authors, and, for bends, algebraic solutions are carried out for the acoustic field and scatteringproperties. Then a study of the soundattenuation in lined bends is given using the multimodal formulation and the properties of such waveguides are shown and discussed, in particular, the presence of a plateau of attenuation at high frequencies and a whispering gallery effect that occurs in bends.

The directivity of acoustic radiation from a rectangular piston arbitrarily located on a rigid prolate spheroidal baffle is formulated. The piston is assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wave functions are obtained using computer programs that have been recently developed to provide accurate values of the wave functions at high frequencies. Results are presented in the form of far-field polar directivity patterns for various piston/spheroid acoustic sizes, piston locations on the spheroid, and spheroidal shapes.

Phenomenological models reproducing the elasticity and acoustic properties of geomaterials and materials with damage have been successfully developed. These models yield macroscopic stress–strain constitutive equations featuring hysteresis with end-point memory, and predict the efficient generation of higher harmonics accompanying the propagation of monochromatic waves. The assumption common to these models is that the material’s microstructure is characterized by nonlinear compliant components of an unspecified nature which can exist in two states: “open” or “closed.” The density of the compliant units is defined on a mathematical continuum (the Preisach–Mayergoyz space) whose elements identify the dynamic behavior of the components. In this work, adhesion is shown to introduce hysteresis with end-point memory in the macroscopic behavior of an interface between two rough surfaces in contact, and, upon scattering, to generate higher harmonics bearing a striking similarity to those observed in wave propagation phenomena in media with distributed damage and in geomaterials. It appears, therefore, that two rough surfaces interacting via adhesion forces offer a meaningful example of macroscopic interface or bond with dynamics resembling that of the fictitious elements of the Preisach–Mayergoyz space, and acoustic nonlinear properties similar to those of rocks and damaged materials.

In the simulation of fluid dynamics, one can either treat the fluid as a continuum or as discrete particles. Although popular for acoustics, the continuum model is limited to small Knudsen numbers (the ratio of mean free path to a length scale). Particle methods are necessary for, but not limited to, problems with Knudsen numbers greater than 0.1, which can occur in shockwaves, microdevices, high frequency sound or rarefied gases. Some well known particle methods include Monte Carlo,cellular automata, discrete velocity, lattice Boltzmann, and molecular dynamics. The direct simulation Monte Carlo (DSMC) method describes gas flows through direct physical modeling of particle motions and collisions. DSMC can model problems for the entire range of Knudsen numbers. In particular, DSMC is capable of simulating nonlinear acoustics, as well as the details of viscous dissipation, dispersion, nonequilibrium effects, and other physical properties. A DSMC method has been implemented for one-dimensional nonlinear acoustics problems on parallel computers using object-oriented and the message passing interface (MPI). DSMC results will be shown and compared with continuum theory and continuum simulations.

Acoustic streaming in ultrasonic (1.4–3.0 MHz) circular and rectangular resonators of path length approximately one-half or one quarter wavelength (λ) has been characterized by particle imagevelocimetry(PIV) using fluorescent 1 μm diam latex markers. Particles of all diameters examined (1, 24, 80 μm) moved into pressure node planes within 4 s of initiation of sonication. The larger particles then moved within that plane to one or more preferred positions. 1 μm particles in a λ/2 cylindrical resonator with a single nodal concentration region for larger particles were convected by Rayleigh-type streaming from the center of the node plane to its edge. In contrast, particles concentrated at many loci in two planes of a second cylindrical and a rectangular chamber. Small scale wall-associated Rayleigh-type vortices occurred in a λ/4 chamber. More unexpectedly, wall-independent bulk suspensionvortices, with circulation planes parallel to the transducer radiating surface, were recorded in both resonators. Tracer particles experienced radial forces that drove them towards or away from the center of the vortices to be concentrated at its center or entrained in a vortex perimeter ring. These different outcomes are discussed in terms of lateral radiation force distribution in the node planes.

A new class of simple, highly efficient, cylindrical acoustic concentration devices has been developed based upon cylindrical (or near cylindrical) geometries [Kaduchak et al., Rev. Sci. Instrum. 73, 1332–1336 (2002)] for aerosol concentration applications. The concentrators are constructed from single PZT tubes driven at or near the breathing mode resonance. Acoustic concentration of aerosols is performed within the tube cavity. It has been found that slight modifications to the cylindrical cavity geometry can significantly increase the collection efficiency and assist in precise particle positioning. This paper analyzes the theoretical framework for the acoustic concentration of particles in these devices for various geometrical perturbations. The cavity geometries studied are (1) hollow cylindrical piezoelectric tube, (2) hollow piezoelectric tube with an inner concentric solid cylinder insert, (3) a hollow piezoelectric tube with a concentric elliptic insert which breaks the circular-cylindrical symmetry, and (4) a hollow elliptic cylindrical piezoelectric tube. It is shown that breaking the circular symmetry within the cavity localizes the particles in small spatial regions within the cavity. This localization of particles may be very useful in applications requiring aerosol collection or particle stream positioning.

The parabolic wave equation (PE) code of Rosenberg [J. Acoust. Soc. Am. 105, 144–153 (1999)] is used as a benchmark to study acoustic propagation in an oceanwaveguide with a rough air/water interface. The PE results allow a close examination of the ability of a ray code [i.e., Gaussian RAy Bundle (GRAB)] to accurately estimate coherent field propagation using a coherent reflection coefficient derived from scattering theory. Comparison with PE implies that the Beckmann–Spizzichino model, as given within the GRAB software package, does not give accurate predictions of the coherent field at long ranges. Three other coherent reflection coefficient approximations are tested: the perturbation, the small slope, and the Kirchhoff approximations. The small slope approximation is the most accurate of the models tested. However, the Kirchhoff approximation is perhaps accurate enough for some purposes and would be simpler to implement as a module within GRAB.

Shallow water bottom reverberation results collected with a hull-mounted sonar exhibit coherenceeffects that manifest themselves as reverberation patterns in time—analogous to the well-known Lloyd mirroreffect that appears in transmission loss as a function of range for shallow sources or receivers. Moreover, the reverberation peaks and nulls arising from the coherent phasing of the propagation paths are evident both in the reverberation envelopes obtained with short pulses and in the matched filter responses for longer pulse lengths. These “coherent” properties of the reverberation deviate from the usual assumptions governing reverberation. Modified assumptions produce coherent reverberation intensity modeled results that match the coherent effects observed in measurements. Finally, the coherent peaks and nulls arising from the phenomenon are shown to produce non-Rayleigh reverberation amplitude distributions in both the measured reverberation and modeled results (increasing the probability of false alarms in this type of interference) unless the reverberation is detrended by the Lloyd mirrorpattern.

A method to obtain coherent acoustic wave fronts by measuring the space–time correlation function of oceannoise between two hydrophones is experimentally demonstrated. Though the sources of oceannoise are uncorrelated, the time-averaged noisecorrelation function exhibits deterministic waveguide arrival structure embedded in the time-domain Green’s function. A theoretical approach is derived for both volume and surface noise sources. Shipping noise is also investigated and simulated results are presented in deep or shallow water configurations. The data of opportunity used to demonstrate the extraction of wave fronts from oceannoise were taken from the synchronized vertical receive arrays used in the frame of the North Pacific Laboratory (NPAL) during time intervals when no source was transmitting.